1. Field of the Invention
The invention concerns a setting device for the fractures of tubular bones, consisting of a longitudinally extended flattened setting element, with an essentially rectangular cross-section, of tissue compatible high-density material, in particular implant steel, in each end section of which there are at least two bores which extend through the opposite wide sides, and bone screws which are guided through these bores.
2. Description of the Related Art
The setting device is most commonly used on fractures of the long tubular bones of the lower extremities.
Operative stabilization of tubular bone fractures has hitherto been carried out by using plate osteosynthesis, marrow pinning (intramedullary nailing) or an external setting device. The choice of the stablilsation procedure is dependent, on the one hand, on the specific type of fracture and, on the other, is decisively determined by the significance that the surgeon attributes to the biomechanical and the biological procedures during the healing of the bone fracture.
The healing of the bone fracture is assisted if there is no relative movement between the two fractured pieces of bone. It is the aim of every conservative and operative measure to minimise these relative movements.
However, recent investigations suggest that this complete immobilisation is not necessary to the same extent in all phases of fracture healing for all directions of movement and, on the contrary, micromovements in the axial direction of the healing of the fractured bone could even be beneficial. Stabilising systems such as the marrow pin and the external setting device do, under certain conditions, permit an axial compression of the fractured bone ends and the forming callus respectively, dependant on the body weight. This method of assisting fracture healing can always be applied following an initial phase if either an uncomplicated type of fracture or the method of setting used means that no shearing stresses or torsion pressures are to be expected in the fracture gap.
The biological aspects of the healing of fractured bones predominantly concern the blood vessel supply to the newly forming bone. In this case, the periosteum which surrounds the outside of all healthy bone, plays a decisive role, but so, too, does the marrow cavity.
It is therefore possible to compile the following requirements for a setting system in the tubular bone area, namely an exclusion of all transverse forces, as well as of flexural and torsional moments, from the area of the fracture, a normal force, which is applied as required, in the area of the fracture, and no additional circulatory disturbances caused by the method of setting in the area of the fracture. The initially mentioned methods of setting only partially fulfil these requirements.
Plate osteosynthesis, whereby a dish-shaped multi-holed plate lies adjacent to the periosteum over a relatively great length, but, most importantly, the area of the fracture, can, because of circulatory disturbances, lead to delays in the healing and to bone necroses.
Marrow pinning or lock nailing, whereby a metal pin which fills the marrow cavity is pushed into the inside of the tubular bone, can likewise lead to considerable circulatory disturbances, though in this case they come from the inside of the tubular bone. A central splintage near the neutral fibre is, in addition, not a good method of protection against alternating flexural stresses in the area of the fracture.
The external setting device is concerned with a stabilising system whereby screws are anchored-proximally and distally related to the fracture area-into the bone and pass to the outside through the skin, where they are connected to a stable force support device. A setting system of this type is not in immediate proximity to the fracture aperture and does not, therefore, lead to circulatory disturbances. There is, however, an important disadvantage in that the transmission of force to the force support device occurs via the bone screws, which are long and therefore elastic in all directions, thus rendering it difficult to estimate the force gradient across the setting device and the bone respectively. A dynamic adjustment according to requirements, i.e. permitting normal forces in a later stage of the healing process of the bone fracture is usually only possible in a limited manner as, due to the large distance between the bone axis and the force support device and to flexural moments in the force support device which is connected therewith, a tilting or jamming of the system usually occurs. In addition an external stabilizing system signifies a considerable danger of infection and requires intensive nursing.
A known stabilization system for fractures in the vertebral area renders possible, by means of its compact construction, implantation under the skin, so that the risk of infections is reduced and patient comfort is improved. However, due to its construction, this rigid system is not suited to the stabilization of tubular bone fractures and with regard to the dynamic alteration possibilities it only offers a gradual improvement in comparison with the external setting system.